The present invention relates to life safety devices, and in particular to hazard detectors such as carbon monoxide and smoke detectors that are typically mounted on walls and ceilings of buildings.
Life safety devices are used in residential and commercial buildings to provide warning to occupants of hazards such as fire or buildup of unsafe gases, such as carbon monoxide. Life safety devices may be powered by a battery assembly that includes a rechargeable battery. The life safety device is connected to a source of AC power, which provides electrical power for charging the rechargeable battery.
When the life safety device reaches the end of its useful life, it may generate a warning signal, such as a chirping sound indicating that it has entered a “trouble” (or “end of life”) mode. This signals the user that it is time to disconnect the life safety device from AC power and throw it away. Rechargeable batteries, such as rechargeable lithium ion batteries, can contain a substantial amount of energy. If not discharged before disposal, they can pose a risk of being damaged and causing a fire and other serious injury. In the case of a life safety device, a rechargeable battery cannot be discharged quickly by shorting the output, because the battery assembly includes a battery protection circuit that will prevent rapid discharge in order to protect the battery. In addition, quickly discharging the battery can cause excessive amounts of heat.
In the past, life safety devices have made use of a mechanical element, such as a switch, to apply a resistance across the battery terminals in order to discharge the battery prior to disposal. A disadvantage of using a switch to discharge the battery is that it relies on the user to actuate the switch. If the user does not actuate the switch, the life safety device and its battery may be disposed of in an unsafe condition.